The bike is a Parlee Chebacco. She might have bought it used, but it does not look ill-used. But cleanliness can conceal problems almost as effectively as dirt does, sometimes. A bike that has been hosed regularly may be clean and shiny, but it has been abused. The abuse is disguised as meticulous care. It only appears to the trained eye in the oxidation, the unnatural dryness of certain areas, and rusty bearings in a bike that otherwise looks like it never leaves the house.
This bike had faint indications of hosing. It's not that old, so it can't have been through much, but the chain was already worn out. It wasn't thrashed, but it was due.
Crank jamming sounds like chain suck, but there were no signs of chain suck. The freehub could be the culprit, if the ratchets lock up and then release, giving her other symptom: no resistance to pedaling. The frame showed absolutely no signs of chain suck. The chainrings had no bends, hooks, or burrs as might result from repeated jamming.
The wheel is a DT Swiss, but not a star ratchet.
Turning to the omniscient Internet to look for reports, rants, and sophomoric proclamations regarding problems with DT freehubs, I discovered one more thing for neurotics to amp about: Points of Engagement. Abbreviated to POE by the cool kids, it's a characteristic worth a lot of chin stroking pronouncements and passionate denunciations.
I guess I don't ride hard enough. But even when I did, I must have been fortunate never to have a serious failure of the drive mechanism. I had one freehub failure in a nearly new Sachs hub in the mid 1990s, when the freehub body itself cracked, causing the ratchet to jam, which fed chain through the system, yanked the derailleur apart, and made me walk home from that ride. The replacement hub that Sachs provided is still working, more than 20 years later. It has outlived its parent company.
In any pawl ratchet, the massive power of your monster quads is channeled through two or three little chips of metal. Points of engagement: two or three at any given moment. The size of teeth in the outer ring is inversely proportional to the number of them. In a star-ratchet type freehub, there are more POE, but the same proportion applies: more points mean smaller points. The engagement is finer, but shallower. The load is spread over more teeth, but a smaller piece of debris can disrupt it.
A freewheeling mechanism at all is a point of weakness compared to a cog threaded directly to the hub shell. Should you let yourself think about it, or just be glad that you've been lucky and hope your luck holds?
Add the POE rabbit hole to the "I'm worried about my position" rabbit hole, with all of its subsidiary burrows: stem length, bar width, seat height, saddle choice, cleat attachment...Does your crank arm length really suit you? Then we can get you losing sleep over the shorts you buy. Have you noticed how the thread count of your tires can cost you as much as a tenth of a second in the sprint? And I don't even want to get started on chain lube.
I was unable to duplicate any of her problems or find any hint of a cause. I cleaned and re-lubed the insides of the freehub, checked the bearings, replaced the chain, and test rode the bike around and around, trying to make it malfunction. It should be fine. But some customers have mysterious powers. You learn never to stand back confidently and say that it's cured, especially with certain people who seem to have their own flock of gremlins constantly sabotaging them.
